1. Field of the Invention
The present invention relates to an optical image measurement device for forming an image of a measured object by using the OCT technology.
2. Description of the Related Art
Recently, attention has focused on an optical image measurement device that forms an image of a measured object by using the OCT (Optical Coherence Tomography) technology. The optical image measurement device splits a low-coherence light into two (lights), and applies one (signal light) of the two to the measured object and the other (reference light) to a reference object. Then, it superimposes the signal light having passed through the measured object and the reference light having passed through the reference object to generate and detect an interference light, and analyzes the detection result to form an image of the measured object (e.g., see Japanese Unexamined Patent Application Publications JP-A 2006-153838 and JP-A 2006-116028).
Since such an optical image measurement device uses an interferometer, it becomes possible to measure with favorable resolving power and sensitivity as compared with other measuring methods. Moreover, since the optical image measurement device performs measurement by using a weak light, there is an advantage of higher safety (less invasive) for a living body.
The optical image measurement device disclosed in JP-A 2006-153838 is called a full-field type or an en-face type. This type of optical image measurement device applies a signal light having a specific beam diameter to a measured object, and thereby forms a tomographic image of a cross section orthogonal to the travel direction of the signal light.
Further, the optical image measurement device disclosed in JP-A 2006-116028 is called a Fourier domain type. This type of optical image measurement device scans an application position of a signal light on a measured object, and thereby forms a depth-wise image at each application position. Then, the optical image measurement device arranges a plurality of depth-wise images, and thereby forms a tomographic image of a cross-section extending in the travel direction (depth direction) of the signal light.
The Fourier domain type uses a coherent light that is temporally low and spatially high. The low temporal coherence secures the resolving power in the depth direction. Moreover, the high spatial coherence causes speckle noise, and limits the resolving power in the direction (horizontal direction) orthogonal to depth direction.
On the other hand, since the full-field type can use a light with low coherence in terms of time and space, it is possible to acquire an image with excellent resolving power in both the depth direction and horizontal direction.
As mentioned above, for an optical image measurement device, it is very important to consider light coherence, in specific, spatial coherence. However, for a conventional optical image measurement device, no efforts have been made to improve measurement with the main aim of spatial coherence.